Treatment of hydrocarbons



H. M. wlam E1- Al.- 2,073,953

TREATMENT 0F HYDROCARBDNS March 16, .1937.

Fiied ocvt. 1s, 1951 ,NVE/viales `40 iiciently, while under -pressure independent of the vapor phase and a portion of the gas is con- 40 'Paalga Mar. 1s, rear c l 2,073,953

UNiTEDsTATEs PATENT ori-loa TREATMENT F HYDBOCARBONS Horace M. Weir and Richard B. Chillas, Jr., Philadelphia, Pa., assignors to The Atlantic Refining Company, Philadelphia, Pa., a corporation oi Pennsylvania Application October 16, 1931, Serial No. 569,220 3 Claims. (Cl. 1903-11)` our invention relates to the treatment of cracking step which otherwise would be gasoline and other volatile hydrocarbons to propated duce liquid fractions substantially free from The invention will be further described with components of excessively high volatility and gas reference to the accompanying drawing in which 5 relatively free from vapors of normally liquid the single figure represents diagrammatically a hydrocarbons. form of apparatus suitable for carryingout our When gasoline, particularly that produced by process. the thermal decomposition of higher boiling oils, The operating conditions of our stabilizing and is condensed inthe presence of the gas which is stripping process are independent oi the condiincident to the gasoline production, equilibrium tions existing in the cracking stage so that the 10 is established between the two phases, whereby a gasoline and gas from any cracking process may portion of the gas is present lin the condensate. be subjected to treatment according to our inwhile the uncondensed gas is saturated with vavention. 'I'he mixture oi gases and vapors from pors of the liquid. The presence of excessively the cracking unit is introduced through the line volatile hydrocarbons in gasoline is undesirable l into the lower end of the iractionating column 15 because of the resultant high vapor pressure A, equipped with bubble plates or other suitable which causes large evaporation losses and may liquid-vapor contacting devices, in which the va-A also cause diiiiculties in the operation of interpors of components less volatile than gasoline nal combustion engines. Y are condensed in a series of pools of liquid of in- Since petroleum gas is for the most part used creasing volatility. The column may be main- 20 as low grade fuel, it is desirable to separate from tained under the operating pressure oi.' the it the normally condensable hydrocarbons asso-A cracking system or may be at a lower pressure, elated therewith to prevent their loss. for example, 40 lbs. per square inch. From4 the Among the objects of our invention are, the lower portion of the column A through the line provision of a unitary system associated with av 2, the least volatile components are removed as 25 cracking process for the stabilization ofthe gasliquid and are returned to the cracking system oline or other light distillates and the recovery for further heat treatment, or are otherwise disoi gasoline-like components from the gas formed posed of, while from the upper end the mixture in the cracking process. A further object of our oi uncondensed vapor's of gasoline and cominvention is to eiect these results with a maxipounds more volatile than gasoline passes 30 mum economy of fuel by using in our process through the line 3 to the condenser B wherein excess heat from the cracking system. A furthe major portion of the gasoline is liqueed and ther object is to carry out the steps of stabillzapasses with the uncondensed portion of the mixtion and recovery of liquid components from the ture through the line 4 into the gas separator C.

gas under conditions entirely independent of the The condensation of the gasoline in the presence 35 cracking conditions and under complete control. of the gaseous reaction products results in es- In accordance with our invention the unstatablishing equilibrium between the liquid and bilized gasoline produced by a cracking process gas whereby a portion of the otherwise condenfollowed by fractional distillation is heated sufsable components of the condensate remain inthe pressure of cracking and fractionating, to tained in the condensate. To prevent the loss of vaporize the undesired components lby passing the valuable portion of the gasoline contained in in indirect heat exchange relationship therewith the gas, the latter is conducted through the line a high temperature liquid fraction withdrawn 5 to the absorber D wherein the gasoline-like from the fractionating zone of the cracking constituents are separated from it as hereinafter 45 process. More particularly in accordance with described. For the separation of the gases conour invention the liquid fraction which serves tained in the gasoline the latter is withdrawn as a heating medium is thereafter utilized as abfrom the separator C t i ough the line 6 from sorbent oil for scrubbing the gas previously sepwhich a portion is forced by the pump 8 through 0 arated from the gasoline, to recover from the gas the line 'l to serve as reflux in the fractionating 50 normally liquid hydrocarbons which occur therecolumn A, while the remainder is conducted by in as vapors, whereupon the enriched absorbent means of the pump l0 to and through the heat oil is returned to the fractionating zone followexchanger F and the line Il to an intermediate ing the cracking process to effect revaporizationpoint in the stabilizing column E. By means oi' 5,5 or the absorbed vapors by waste heat or the the pump I ll the wild" gasoline may be forced into the stabilizing column under any pressure which it is desired to maintain therein. It is generally advisable to conduct the stabilization under a higher pressure than exists in the fractionating column of the cracking stage in order that proper separation of gas and vapors may be effected. Our process is particularly adapted to such independent operation.

In this stabilizer the gasoline, containing the more volatile components, countercurrent to and in direct heat-exchange relation with rising vapors produced from the gasoline at the base of the column by passing a heating medium through the coil 24 as hereinalter described. From the base of the column, stabilized gasoline, freed in the column of its more volatile components, is withdrawn through the line I2 and is cooled in the heat exchanger F and the Vwater cooler K and is then conducted through the line I4, controlled by valve I4', to storage.

The vapors and gases evolved from the gasoline in the stabilizer are fractionated in its upper portion by contact with reflux obtained by passing the residual vapors and gases from the top of the column to the condenser G. Pressure, for example lbs. per sq. in., is maintained on the stabilizer E by means of the valve I1' in the line I1. This pressure should be such that, with the particular gasoline under treatment, the available cooling medium, generally water, will condense enough of the hydrocarbons removed from the gasoline during the stabilization process to form sufficient reflux to fractionate the gases and vapors in the'stabilizing column closely enough so that the gas will be substantially free from components which are desired in the gasoline. Gasoline produced by cracking gas oil from a Mid-continent crude at about 925 F. under a pressure of approximately 850 lbs. ls satisfactorily stabilized by heating in the base of the stabilizer to about 350 F. while maintaining a pressure of 175 lbs. per sq. in. on the system.

The gas which passes uncondensed through the condenser G is conducted from the gas separator H through the line II to the line 3| and through it to storage. If desired, a portion of the reflux returned to the stabilizer E may be withdrawn, as for example, through the lines 20 or 22, and used as fuel in the form of liquefied gas.

The heating of the gasoline in the stabilizing column is effected by withdrawing from the fractionating column A through the line 23 for example, a high temperature liquid fraction of suitable characteristics for later use as absorbent oil and passing the liquid so removed through the coil 24 in the base of the column E. The withdrawal of liquid from the fractionating column is controlled by valve 23'. The heating medium which may be, for example, at 500 F., transmits heat to the gasoline in the base of the column and is itself correspondingly reduced in temperature, for example to about 360 F. The oil fraction utilized as a source of heat then passes through the line 25 to the heat exchanger J wherein it is further cooled and finally, by means of the water cooler K', it is reduced to a temperature suitable for use as absorbent oil in the absorber D to the upper end of which it is introduced through the line 29. The absorbent oil passes through the absorber D countercurrent to, and in direct contact with, the rich gas from the separator C and absorbs from the gas the components of gasoline-like characteristics, with passes downwardly the result that the gas leaving the top of the absorber D through from these components and is termed dry gas. Valve 3|' controls pressure on the absorber.

From the bottom of the absorber D the enriched absorbent oil is conducted by pump 34 through the line 33 to and through the heat exchanger J, wherein it serves to cool the partially cooled stream of lean absorbent oil leaving the heating coil 24 and is itself preheated. It is then introduced through the line 31 into the fractionating column A above the vapor inlet I. The temperature at which cracking occurs is so greatly in excess of the vaporizing temperature of gasoline that considerable quantities of excess heat are available. Advantage is taken of this surplus heat by introducing the rich absorbent oil into direct contact with the cracked vapors in the column A, thereby vaporizing the absorbed low boiling hydrocarbons which commingle with the gases and vapors introduced from the cracking system through the line I into the fractionating column A. If necessary, additional absorbent oil, for example, charging stock for the cracking still, may be introduced into the top of the absorber through the line 32 and also additional heat may be introduced into the base of the stabilizing column E by passing any suitable heating medium, for example, residual oil from the cracking still or superheated steam through the coil 42 by means of the inlet and outlet lines 43 and 44 respectively. The lines 38 and 39 permit bypassing the coil 24.

Thus it will be seen that we have provided a process whereby the volatile gasoline produced in a cracking process is freed from the undesirable gases and low boiling components without the loss of any of such constituents, while at the same time the gas normally occurring in cracking processes is freed from its content of gasoline-like constituents. These results, moreover, are accomplished without requiring the use of any heat other than that which occurs in the cracking process and would be otherwise lost in the cooling Water, thereby effecting a saving of fuel.

It is to be understood that although a single side-stream drawoff is shown for removing a liquid fraction from the column to serve as heating medium in the coil 24 and as absorbent oil, the process is not to be limited to any particular oil for this purpose, but our invention comprehends even the use of a portion of the recycle stock for this purpose, conducting it through line 26, controlled by valve 26', to line 23.

It is characteristic of our process that the stabilization step and the cracking and fractionation of the cracked products are entirely independent of each other insofar as pressure is concerned. As a result, the cracking operation may be conducted under any pressure conditions most favorable for the cracking process and these conditions, as well as the pressure under which the vapors are fractionated, may be changed without varying the stabilizer pressure; at the same time, if it is desired to change the volatility of the stabilized gasoline by varying the pressure on the stabilizer, this may be done without affecting the cracking or fractionating conditions.

This process is primarily intended for use with the products of cracking petroleum or other hydrocarbons since such processes normally produce considerable quantities of gas line 3| is substantially free.

and since the'cracked vapors in the fractionating tower contain large quantities of excess heat. However, it is also applicable to the products resulting from distilling hydrocarbon o'ils including coal tar, by means of a pipe still and fractionating, column or other distillation equipment in whichexce'ss heat is available.

In the appended claims the terms stabilizing and stabilization are used to designate the process in which liquid condensate containing gas and low boiling liquids is subjected to controlled heating under regulated pressure to remove therefrom undesired quantities of low boiling constituents; also the term stripping is used to designate the process in which gas containing vapors of constituents desired inthe liquid condensate is scrubbed with an absorbent l oil.

What we claim is: 1. 'I'he process of refining petroleum products which comprises introducing into a fractionating zone a mixture of gas, vapors of gasoline and vapors of hydrocarbons less volatile than gasoline, fractionally condensing therein the vapors less volatile than gasoline, passing the mixture of gas and gasoline vapors from the fractionating zone to a condensing zone where- V 4conducting uncondensed portions of'the gasin the major portion of the gasoline is liquefied,

vapor mixture to an absorbing zone, introducing the liquefied gasoline into .a stabilizing zone, withdrawing from the fractionating zone a liquid fraction less volatile than gasoline, passing it without previous substantial reduction in temperature through theY stabilizing zone in-indirect heat-interchange relation with the gasoline 'to distill therefrom volatile components and to cool said liquid fraction, thereafter further reducing the temperature of said liquid fraction and passing itinto direct contact with the uncondensed portions of the gas-vapor mixture in the absorbing zone, -withdrawing therefrom said fraction enriched with that portion of the gas-vapor mixture absorbed therein and returning the enriched fraction to an intermediate point in the fractionating zone vaforesaid above inlet.

2. The 'process of rening petroleum products which comprises introducing into a fractionating zone a mixture of uncondensable gas, vapors of gasoline and vapors of hydrocarbons less volatile than gasoline, fractionally condensing therein the vapors less volatile than gasoline, passing the mixture of gas and gasoline vapors the vapor 3 from the fractionating zone to a condensing zone wherein the major portion of the gasoline is '*l'iqueiied, conducting uncondensed portions of the gas-vapor mixture to an absorbing zone, introducing the liquefied gasoline into a stabilizing zone, withdrawing from the fractionating Vzone a liquid fraction less volatile than gasoline, passing it without previous substantial reduction in temperature through the stabilizing zone in indirect heat interchange relation with the gasoline to distill therefrom volatile components and to cool said liquid fraction, thereafter further reducing the temperature of said liquid fraction and passing it into direct contact with the uncondensed portions of the gasvapor mixture in theV absorbing zone, withdrawing therefrom said fraction enriched with that portion of the gas-vapor mixture absorbed thereinand returning the enriched fraction to.

an intermediate point in the fractionating zone aforesaid while maintaining in the stabilizing zone'a pressure independent of that maintained in the fractionating zone.

3. The process of lrefining petroleum products which comprises introducing into a fractionating zone a mixture of gas, vapors of gasoline and vapors of hydrocarbons less volatile-than gasoline, fractionally condensing therein the vapors less volatile than gasoline, passing the mixture of gas and gasoline vapors from the fractionating zone to a condensing zone wherein the major portion of the gasoline is liquefied, conducting uncondensed portions of the gas-vapor mixture-to an absorbing zone, introducing the liquefied gasoline into a stabilizing zone, withdrawing from the fractionating zone a liquid fraction less volatile thanI gasoline, passing it without previous substantial reduction in temperature through theA stabilizing zone in indirect heat-interchange relation with the gasoline to distill therefrom volatile components and to cool said liquid fraction, thereafter further reducing the temperature of said liquid fraction and passing it into direct contact with the uncondensed portions of the gas-vapor mixture in the absorbing zone, withdrawing therefrom said fraction enriched with that portion of the gas-vapor mixture absorbed therein and vaporizing the absorbed constituents by heat contained in the mixture of gas, vapors of gasoline and vapors of hydrocarbon less volatile than gasoline. 

